The present invention relates to electronic musical instruments, and more particularly to improvements in means for expanding the dynamic volume range of such instruments. Still more particularly, the invention relates to improvements in electronic musical instruments of the type wherein envelope control voltage signals are generated in response to depression of keys and the intensity of such signals is a function of the length of intervals which elapse during movement of keys from non-depressed to depressed positions.
It is already known to construct an electronic piano (e.g., the 1974 version of the so-called Effekt-Piano manufactured by the West German firm WERSI) in such a way that the velocity of movement of a key from non-depressed to depressed position (i.e., the force which is applied to move the key between such positions) determines the length of the interval of discharge of a capacitor in the means for generating envelope control voltage signals. The capacitor is charged while the key is held in the non-depressed position. To this end, the capacitor is connected with a source of starting potential while the key assumes its normal (non-depressed) position, and the capacitor is connected with the ground when the key completes its movement to depressed position. Thus, the extent of discharge of the capacitor is a function of the length of interval of movement of the respective key to depressed position. If the interval is relatively short, the amplitude of the thus generated envelope control voltage is relatively low and the volume of the tone is also low. The means for amplifying tone signals is a transistor which conducts in response to the application of a certain minimum voltage (approximately 0.5 volt). Since the maximum remaining potential of the capacitor is not in excess of 10 volts, the application of a supply voltage in the range of 15 volts allows for a variation of the tone volume signal at a ratio of 20:1 which corresponds to a maximum achievable dynamic effect of approximately 26 decibels.
In a mechanical piano or a concert piano, the dynamic volume range is substantially greater; it is normally between 40 and 60 decibels which corresponds to volume differences of 100:1 to 1000:1.